My grateful thanks for the wealth of information and 
assistance offered by Rolf Dessauer, Dave Gants,
Tomas Stohr  and  Bob Allison (those websites are 
wonderful).
I hope to try both the Dylux and digital camera methods---
both techniques quite new to me, but less likely to panic 
our physicists than my old radio-active source method 
(which was like working in a deep-sea diving suit 
anyway). Do the rest of you using beta-radiography go
though this?
(I used to wave a u.v. lamp around quite happily, too, 
until they insisted on kitting me out with visors, gloves, 
tongs and heaven knows what-all.)
What a splendid List!
Avril 
---------------------------------------
  e-mail: A.K.Henry@exeter.ac.uk
     tel: 01392 264252
     fax: +44 1392 264361
   snail: Professor Avril Henry, School of English & American Studies,
          Queen's Building, Queen's Drive, University of Exeter,
          EXETER, UK, EX4 4QH
Robert W. Allison
Dept. of Philosophy & Religion, Bates College and
James Hart
Information Services, Bates College Lewiston, Maine, 04240